This invention relates to a system for preventing the discharge to the atmosphere of fuel vapor generated in a fuel tank for an internal combustion engine.
A kind of system designed to make a canister adsorb fuel vapor generated in a fuel tank for an internal combustion engine of a vehicle or the like and thereafter to extract and supply the adsorbed fuel vapor for the combustion effected by the engine has previously been known, such as that as disclosed in U.S. Pat. No. 3,884,204. This patent was made in consideration of the different states of fuel vapor which can exist, such as that observed when vapor is discharged from the tank during refueling and that observed at other times, and it therefore provides separate canisters for processing accordingly.
It is an object of the present invention to provide a system with a simple construction having only one canister adapted for the different states of fuel vapor being discharged from the tank at the time of refueling and at other times. To this end, the present invention provides a system having a first channel through which fuel vapor passes from the top of a fuel tank to a canister at all the times other than during refueling, a second channel through which fuel vapor passes from the neck of a refueling opening portion of the tank to the canister, a purge channel formed from the canister to a suction channel of the internal combustion engine, a first three-way electromagnetic valve disposed in the second channel, and a second three-way electromagnetic valve disposed in the purge channel, wherein the first electromagnetic valve is operated to open the second channel during the shut-down state of the engine and, during the operation of the engine, to close the channel on the tank side while opening the channel on the canister side to the atmosphere, and wherein the second electromagnetic valve is operated to open the channel on the side of the canister to the atmosphere during the shut-down state of the engine and to open the purge channel during the operation of the engine.
Other and further objects, features and advantages of the invention will appear more fully upon reading the following description.